Some known vehicle air-conditioners include an outside air passage and an inside air passage that are provided separately for guiding outside air and inside air, respectively. In a heat mode or a heat/defrost mode, the known vehicle air-conditioners circulate the inside air, having been already heated within a passenger compartment of the vehicle, through the inside air passage and blow the circulated inside air from heat outlets as a conditioned air to thereby heat the passenger compartment at a proper temperature. At the same time, the outside air is introduced into the outside air passage to generate a conditioned air having a low level of humidity and the conditioned air is blown from defrost nozzles toward windowpanes to keep good antifogging property of the windowpanes.
By virtue of the outside air passage and the inside air passage that are provide separately, the known vehicle air-conditioners are able to improve passenger-compartment heating power or capacity and secure good windowpane anti-fogging property in the heat mode or the heat/defrost mode. One example of such known vehicle air-conditioners is disclosed in Japanese Patent No. 3684712 corresponding to Japanese Patent Application Laid-open Publication (JP-A) No. 10-109520.
However, when a bi-level mode or a heat mode is selected, the disclosed vehicle air-conditioner is not able to blow the outside air and the inside air concurrently, via the outside air passage and the inside air passage, respectively, into the passenger compartment while it is operating in a normal stable stat. The term “normal stable state” is used herein to refer to a state in which the volume of conditioned air blown into the passenger compartment and the temperature of the passenger compartment are set in an intermediate range.
Thus, while the disclosed vehicle air-conditioner is operating in the normal stable state in the bi-level mode or the hat mode, one of the outside air and the inside air is solely used to generate conditioned air to be blown into the passenger compartment. This arrangement makes it difficult to achieve a good balance between passenger-compartment temperature comfort and windowpanes anti-fogging property. To deal with this problem, during a normal stable state operation, the conditioned air generated solely from the outside air or inside air is heated or cooled before being blown into the passenger compartment. Such additional heating or cooling will increase energy consumption of the vehicle air-conditioner.